1. Field of the Invention
The present invention relates to a method and apparatus for forming an organic thin film which is to be the main component of a device useful in the fields of semiconductors and optical technology, for example. More particularly, the present invention pertains to a method and apparatus for forming a monomolecular film or a built-up monomolecular film of an organic substance on a substrate.
2. Description of the Prior Art
Conventionally, development of materials employed in the semiconductor and optical technological fields has involved inorganic substances, owing to their relative ease in handling.
Recently, however, organic chemists have achieved remarkable technical developments in the semiconductor and optical fields. It have now been proposed to use an organic thin film in place of the conventionally-employed inorganic thin film in integrated circuit devices such as logic elements, memory elements or photoelectric conversion elements, and in optical devices such as microlens arrays or optical waveguides.
Such organic thin films can be manufactured by a conventional monomolecular build-up method. In this method (which is also called, "Langmuir-Blodgett's Technique", or "LB Technique"), molecules having hydrophilic and hydrophobic groups are evenly spread over the surface of water by taking advantage of the hydrophilic and hydrophobic nature of the molecules so as to form a monomolecular film. This film is then transferred onto the surface of a substrate, thus making it possible to form a monomolecular film or a built-up monomolecular film in which molecules are built up on top of each another. Hereafter, these films are each called, "LB film" as illustrated in U.S. Pat. No. 4,511,604.
The conventional apparatus for forming LB films, as shown in FIG. 4, includes a square-shaped shallow, but wide, water tank 1 and a frame 2 which is disposed in the tank such that it horizontally encloses a water surface 3. The frame 2 functions as a two-dimensional cylinder, and its interior is provided with a square-shaped float 4 which has a width slightly smaller than the internal dimension of the frame 2. Float 4 serves as a two-dimensional piston and smoothly moves to the right and left, as illustrated in FIG. 4. In order to move the float 4 in both directions, float 4 is connected by a wire 5 to a winder 6 which is driven by a motor or the like.
To form a monomolecular film, a film-forming substance is dissolved in a volatile solvent, such as benzene or chloroform, and the solution is then dropped onto the surface 3 of the water. After the solvent has evaporated, a monomolecular film which exhibits two-dimensional behavior remains on the surface 3. When the areal density of the molecules is low, the film can be designated a gaseous film and is constituted of a two-dimensional gas. As the molecules spread over the water surface 3 are condensed and the areal density of the molecules is increased by moving the float 4 to the right, as viewed in FIG. 4, the interactions among the molecules are intensified. The gaseous film is then transformed into a two-dimensional liquid film and then, if the density of the molecules is further increased, into a two-dimensional solid film. In such a solid film, the molecules are oriented and show a high degree of order. Accordingly, the oriented and ordered molecules form a uniform and very thin film, which film properties are essential for a component of a semiconductor device.
The thus-formed monomolecular film is transferred from the surface 3 of the water onto a substrate 7 in a vertical dip process. The vertical dip process is conducted by moving substrate 7 mounted on holder 8 in a vertical direction 9 perpendicular to the surface of the water, while retaining the monomolecular film on the surface 3 under a surface pressure of a predetermined value which is suitable for forming a built-up film. Three types of films can be built up by this process an X type, formed by depositing a monomolecular film 10 on the substrate 7, when the substrate 7 is merely dipped into the water, as shown in FIG. 5 (a); a Y type, formed by depositing the monomolecular film 10, when the substrate 7 is both dipped into and withdrawn from the water, as shown in FIG. 5 (b); and a Z type, formed by depositing the monomolecular film 10, when the substrate 7 is just drawn out of the water, as shown in FIG. 5 (c). In each molecule shown in FIG. 5, reference numeral 11 denotes its hydrophilic group, and 12, its hydrophobic group.
Another process for transferring the monomolecular film onto the surface of the substrate is represented by the horizontal deposition process (not shown). In this process, the substrate is moved vertically with respect to the surface 3 of the water with the substrate surface upon which the film is to be deposited being disposed substantially parallel to the surface of the water, as the monomolecular film is deposited.
The above-described conventional processes of transferring a monomolecular film have a disadvantage in that the device for moving the substrate in the vertical direction employs a motor with gears or the like. The vibrations produced by this motor are transmitted to the substrate so that the deposition of the monomolecular film is not even.